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    Weekly Report: Influenza Summary Update

    2008-2009 Influenza Season Week 44, ending November 1, 2008

    (All data are preliminary and may change as more reports are received.)

    Synopsis:

    During week 44 (October 26-November 1, 2008), a low level of influenza activity was reported in the United States.

    • Eleven (0.6%) specimens tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories, and reported to CDC/Influenza Division, were positive for influenza.
    • The proportion of deaths attributed to pneumonia and influenza (P&I) was below the epidemic threshold.
    • The proportion of outpatient visits for influenza-like illness (ILI) was below national and region-specific baseline levels.
    • Fifteen states, the District of Columbia, and Puerto Rico reported sporadic influenza activity; 35 states reported no influenza activity.

    National and Regional Summary of Select Surveillance Components

    Region
    Data for current week Data cumulative for the season
    Out-patient ILI* % positive for flu† Number of jurisdictions reporting regional or widespread activity‡ A (H1) A (H3) A Unsub-typed B Pediatric Deaths
    Nation Normal 0.6 % 0 of 51 16 9 55 23 0
    New England Normal 0.0 % 0 of 6 0 0 0 0 0
    Mid-Atlantic Normal 0.2 % 0 of 3 1 0 2 0 0
    East North Central Normal 0.0 % 0 of 5 0 0 0 0 0
    West North Central Normal 0.0 % 0 of 7 0 0 0 0 0
    South Atlantic Normal 1.7 % 0 of 9 2 2 15 10 0
    East South Central Normal 0.0 % 0 of 4 0 0 0 0 0
    West South Central Normal 2.4 % 0 of 4 2 0 16 4 0
    Mountain Normal 1.2 % 0 of 8 0 7 3 3 0
    Pacific Normal 1.9 % 0 of 5 11 0 19 6 0

    * Elevated means the % of visits for ILI is at or above the national or region-specific baseline
    † National data is for current week; regional data is for the most recent three weeks.
    ‡ Includes all 50 states and the District of Columbia

    U.S. Virologic Surveillance:

    During week 44, WHO and NREVSS laboratories located in all 50 states and Washington D.C. reported 1,780 specimens tested for influenza viruses, 11 of which were positive: two influenza A (H1) viruses (West South Central region), one influenza A (H3) virus (Mountain region), seven influenza A viruses that were not subtyped (Mid-Atlantic, South Atlantic, and West South Central regions) and one influenza B virus (South Atlantic region).

    INFLUENZA Virus Isolated
    View Chart Data | View Full Screen

    Antigenic Characterization:

    CDC has antigenically characterized one influenza virus collected by U.S. laboratories since October 1, 2008. The influenza B virus was characterized as B/Florida/04/2006-like, belonging to the B/Yamagata lineage. Influenza B viruses currently circulating can be divided into two antigenically distinct lineages represented by the B/Yamagata/16/88 and B/Victoria/02/87 viruses. The recommended influenza B component for the 2008-09 influenza vaccine is a B/ Florida/04/2006-like virus, belonging to the B/Yamagata lineage.

    In addition, a small number of isolates from specimens collected during September were available for antigenic characterization: two influenza A (H3N2), and four influenza B viruses. All six viruses were antigenically similar to the components selected for the 2008-09 influenza vaccine (A/Brisbane/10/2007-like (H3N2), and B/Florida/04/2006-like).

    It is too early in the influenza season to determine which influenza viruses will predominate or how well the vaccine and circulating strains will match.

    Pneumonia and Influenza (P&I) Mortality Surveillance

    During week 44, 6.6% of all deaths reported through the 122-Cities Mortality Reporting System were due to P&I. This percentage is below the epidemic threshold of 6.7% for week 44.

    Pneumonia And Influenza Mortality
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    Influenza-Associated Pediatric Mortality

    No influenza-associated pediatric deaths were reported during week 44.

    Influenza-Associated Pediatric Mortality
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    Influenza-Associated Hospitalizations

    Laboratory-confirmed influenza-associated hospitalizations are monitored in two population-based surveillance networks: the Emerging Infections Program (EIP) and the New Vaccine Surveillance Network (NVSN). EIP and NVSN estimated rates of hospitalization for influenza will be reported every two weeks starting later this season.

    Outpatient Illness Surveillance:

    During week 44, 1.0% of patient visits reported through the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) (formerly known as the U.S. Influenza Sentinel Provider Surveillance Network) were due to influenza-like illness (ILI). This percentage is less than the national baseline of 2.4%. On a regional level, the percentage of visits for ILI ranged from 0.5% to 1.9%. All nine regions reported percentages of visits for ILI below their respective region-specific baselines.

    national levels of ILI and ARI
    View Chart Data |View Full Screen

    Geographic Spread of Influenza as Assessed by State and Territorial Epidemiologists:

    During week 44 the following influenza activity was reported:

    • Sporadic activity was reported in the District of Columbia, Puerto Rico and 15 states (Alaska, California, Colorado, Connecticut, Delaware, Hawaii, Idaho, Illinois, Indiana, Massachusetts, Nevada, New York, Pennsylvania, Texas, and Utah).
    • No influenza activity was reported in 35 states (Alabama, Arizona, Arkansas, Florida, Georgia, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, New Hampshire, New Jersey, New Mexico, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Rhode Island, South Carolina, South Dakota, Tennessee, Vermont, Virginia, Washington, West Virginia, Wisconsin, and Wyoming).

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    A description of surveillance methods is available at: http://www.cdc.gov/flu/weekly/fluactivity.htm

    • Page last updated November 7, 2008.
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